Chapter 11: Chemical Bonding I: Basic Concepts

Transcription

1 General Chemistry Principles and Modern Applications Petrucci Harwood Herring 8 th Edition Chapter 11: Chemical Bonding I: Basic Concepts Philip Dutton University of Windsor, Canada N9B 3P4 Prentice-Hall 2002

2 Contents 11-1 Lewis Theory: An Overview 11-2 Covalent Bonding: An Introduction 11-3 Polar Covalent Bonds 11-4 Writing Lewis Structures 11-5 Resonance 11-6 Exceptions to the Octet Rule 11-7 The Shapes of Molecules 11-8 Bond Order and Bond Lengths 11-9 Bond Energies Focus on Polymers Macromolecular Substances Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 2 of 35

3 11-1 Lewis Theory: An Overview Valence e - play a fundamental role in chemical bonding. e - transfer leads to ionic bonds. Sharing of e - leads to covalent bonds. e - are transferred of shared to give each atom a noble gas configuration the octet. Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 3 of 35

4 Lewis Symbols A chemical symbol represents the nucleus and the core e -. Dots around the symbol represent valence e -. N P Si As Sb Bi Al Se I Ar Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 4 of 35

5 Lewis Structures for Ionic Compounds BaO O Ba Ba O MgCl 2 Mg Cl Cl Mg 2+ 2 Cl - Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 5 of 35

6 11-2 Covalent Bonding Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 6 of 35

7 Coordinate Covalent Bonds H H N H H Cl H H N H H + Cl - Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 7 of 35

8 Multiple Covalent Bonds O C O O C O O C O O C O Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 8 of 35

9 Multiple Covalent Bonds N N N N N N N N Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 9 of 35

10 11-3 Polar Covalent Bonds δ+ δ- H Cl Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 10 of 35

11 Analogy to Population Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 11 of 35

12 Electronegativity Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 12 of 35

13 Percent Ionic Character Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 13 of 35

14 Writing Lewis Structures All the valence e - of atoms must appear. Usually, the e - are paired. Usually, each atom requires an octet. H only requires 2 e -. Multiple bonds may be needed. Readily formed by C, N, O, S, and P. Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 14 of 35

15 Skeletal Structure Identify central and terminal atoms. H H H C C O H H H Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 15 of 35

16 Skeletal Structure Hydrogen atoms are always terminal atoms. Central atoms are generally those with the lowest electronegativity. Carbon atoms are always central atoms. Generally structures are compact and symmetrical. Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 16 of 35

17 Strategy for Writing Lewis Structures Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 17 of 35

18 Formal Charge 1 FC = # valence e- -# lone pair e- - # 2 bond pair e- Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 18 of 35

19 Example 11-6 Writing a lewis Structure for a Polyatomic Ion. Write the Lewis structure for the nitronium ion, NO 2+. Step 1: Total valence e - = = 16 e - Step 2: Plausible structure: O N O Step 3: Add e - to terminal atoms: O N O Step 4: Determine e - left over: = 0 Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 19 of 35

20 Example 11-6 Step 5: Use multiple bonds to satisfy octets. O N O + O=N=O Step 6: Determine formal charges: 1 FC(O) = 6-4 (4) = FC(N) = 5-0 (8) = +1 2 Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 20 of 35

21 Alternative Lewis Structure O N O O N O 1 FC(O ) = 6-2 (6) = FC(N) = 5-0 (8) = FC(O ) = 6-6 (2) = -1 2 Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 21 of 35

22 Alternative Lewis Structures Sum of FC is the overall charge. FC should be as small as possible. Negative FC usually on most electronegative elements. FC of same sign on adjacent atoms is unlikely. + + O N O - Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 22 of 35

23 Example 11-7 Using the Formal Charge Concept in Writing Lewis Structures. Write the molst plausible Lewis structure of nitrosyl chloride, NOCl, one of the oxidizing agents present in aqua regia Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 23 of 35

24 11-5 Resonance O O O O O O -½ O O O + -½ Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 24 of 35

25 11-6 Exceptions to the Octet Rule Odd e - species. N=O H H C H O H Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 25 of 35

26 Exceptions to the Octet Rule Incomplete octets. F F F F B F + F B - F F + - B F Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 26 of 35

27 Exceptions to the Octet Rule Expanded octets. F Cl Cl F F Cl Cl S P P F F Cl Cl Cl Cl F Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 27 of 35

28 Expanded Valence Shell Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 28 of 35

29 11-7 The Shapes of Molecules H O H Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 29 of 35

30 Terminology Bond length distance between nuclei. Bond angle angle between adjacent bonds. VSEPR Theory Electron pairs repel each other whether they are in chemical bonds (bond pairs) or unshared (lone pairs). Electron pairs assume orientatioins about an atom to minimize repulsions. Electron group geometry distribution of e - pairs. Molecular geometry distribution of nuclei. Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 30 of 35

31 Balloon Analogy Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 31 of 35

32 Methane, Ammonia and Water Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 32 of 35

33 Table 11.1 Molecular Geometry as a Function of Electron Group Geometry Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 33 of 35

34 Applying VSEPR Theory Draw a plausible Lewis structure. Determine the number of e - groups and identify them as bond or lone pairs. Establish the e - group geometry. Determine the molecular geometry. Multiple bonds count as one group of electrons. More than one central atom can be handled individually. Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 34 of 35

35 Dipole Moments Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 35 of 35

36 Dipole Moments Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 36 of 35

37 Bond Order and Bond Length Bond Order Single bond, order = 1 Double bond, order = 2 Bond Length Distance between two nuclei Higher bond order Shorter bond Stronger bond Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 37 of 35

38 Bond Length Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 38 of 35

39 Bond Energies Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 39 of 35

40 Bond Energies Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 40 of 35

41 Bond Energies and Enthalpy of Reaction H rxn = 3 H(product bonds) - 3 H(reactant bonds) = 3 H bonds formed - 3 H bonds broken = -770 kj/mol (657 kj/mol) = -114 kj/mol Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 41 of 35

42 Focus on Polymers Macromolecular Substances Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 42 of 35

43 Chapter 11 Questions 1, 4, 6, 8, 10, 11, 15, 27, 33, 37, 53, 57, 65 (also calculate formal charges), 71, 86, 94 Prentice-Hall 2002 General Chemistry: Chapter 11 Slide 43 of 35